Cubic boron nitride is extremely hard having a Vickers hardness of about 5000. Its hardness makes cubic boron nitride useful in a variety of industrial components.
Abrasive particles, such as cubic boron nitride particles, have been extensively used for cutting, grinding, lapping and polishing in metal removing industries as well as in medical fields such as dentistry and surgery. Abrasive particles are used in abrasive tools such as grinding and dressing wheels, crowns and single point tools. Considerable amount of research has gone into improving the bonding properties of cubic boron nitride to the matrices of these tools since poor bonding at the cubic boron nitride/matrix interface leads to dislodgement of the cubic boron nitride particle from the matrix during the abrading operation. As a result of this research, it is known in the art that the metal coating of abrasive particles improves the retention of such particles in the matrices of various abrasive tools, such as resin bonded wheels. In particular it is known that the retention of cubic boron nitride particles is improved with nickel coating. To improve the retention of cubic boron nitride particles, their surfaces are provided with a rough textured nickel coat having jagged edges. The jagged edges provide the metal coated particles improved mechanical interlocking means with which to retain them in the resin matrix during the abrading operation. The metal coat also provides means for evenly transfering heat generated along the surfaces of the abrasive particles during the abrading action. However metal layers have poor adhesion to cubic boron nitride.
It is also known in the art that the retention of cubic boron nitrides in the abrasive tools is further improved by providing the particles with multiple layers of metals, such as molybdenum, titanium, niobium, chromium, zirconium, copper and nickel.
The metal coating of the particles may be achieved by a variety of methods depending on the nature of the metal coating. The metal coating may be applied under high temperature, by well known processes, such as chemical vapor deposition, molten salt deposition and powder agglomeration coating. The main drawback of such techniques is that the high process temperatures can significantly degrade the abrasive particles. The aforementioned problem of degradation may be somewhat obviated by electrolytically, electrolessly or vacuum depositing the metal coating on abrasive particles, however the problem of poor adhesion to cubic boron nitride still remains.
The present invention is directed to improving adhesion of metal coats to the surfaces of cubic boron nitride particles.